1. Field of the Invention
The present invention relates to closure caps in general, and in particular to closure caps which have improved sealing capability. The caps can be categorized as unitary caps having two dissimilar materials for sealing purposes.
2. Prior Art
A closure cap which provides a vacuum seal for containers, and especially for containers of varying wall thickness and irregularities, such as chips and the like around the rim of the container, is known from U.S. Pat. No. 4,143,785. In this patent, the closure cap is disclosed as including a pair of flexible annular flanges adapted to engage the inner and outer edges of the upper rim of the container to be closed to provide a vacuum seal when the cap is placed on the container. The two flanges are concentrically arranged, with the outer flange being canted outwardly and the inner flange being canted inwardly. This angled arrangement provides for a line contact rather than a surface contact with the container rim. The two flanges are disclosed as working independently to produce the desired contact. An improvement over this closure cap is found in U.S. Pat. No. 4,308,965. In this latter patent, the closure cap is disclosed as constructed of two dissimilar plastic materials forming a substantially rigid outer member and a substantially resilient inner sealing member, with the inner sealing member being anchored to the outer member. The use of two dissimilar materials in the manner described in the latter noted patent is referred to as a two-shot design. Like the cap disclosed in the 4,143,785 patent, the closure cap disclosed in the 4,308,965 patent includes a pair of flexible annular flanges adapted to engage the inner and outer edges of the upper rim of the container to be closed to provide a vacuum seal when the cap is placed on the container. This design is intended to have the same range of application in terms of container sizes as that disclosed in the 4,143,785 patent, and it was believed that the spacing of two flanges with respect to each other and the top wall of the container was not critical due to the resiliency of the flanges. For this reason, the particular configuration of the design disclosed in the 4,038,965 patent was dictated primarily by fabrication considerations rather than by any dimensional considerations. In fact, it has been found that the intended range of application of this design is limited, and while it is not clear why this is so, corrective action was deemed warranted since this design has proved quite successful for a limited range of container sizes.
It would therefore be desirable to enhance the two-shot design disclosed in the 4,308,965 patent by giving it a greater range of application.